I live in White Plains and am with Full Circle/Phelps but I researched other options because I'm attempting a VBAC and wanted a hospital that was open to natural birth. This is information I got from my doula and the midwives at Full Circle and friends.
As PP said, I have heard great things about CT Birth Center in Danbury but it is really far (close to 1 hour one way drive) from White Plains and I decided against going there because I didn't want to drive so far for prenatal appointments.
In Westchester, there is also a small practice of 2 ob/gyns Dr. Dennis McGroary and Dr. Susan Malley based out of Katonah and Yorktown. I believe they deliver at Northern Westchester Hospital in Mt. Kisco.
There is a midwife/ob-gyn group Westchester Medical Practice in Putnam Valley (about 45 min from White Plains) who deliver at Hudson Valley Hospital.
I have heard that both Northern Westchester Hospital and Hudson Valley Hospital are "natural birth" friendly. White Plains Hospital, while nice, is not well known for being natural birth friendly, though I'm sure you can have a natural birth there. I don't know about Lawrence, though I have heard that their maternity floor is very nice. Greenwich Hospital is also nice and several friends have had natural births there. There is an ob/gyn group in Rye called WestMed whose doctors deliver there, but it is a typical big ob/gyn practice with long waits during prenatal appts etc.